What to know about a second covid booster shot

Vials of the Moderna and Pfizer-BioNTech coronavirus vaccines. (Charles Krupa/AP)
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Federal officials Tuesday authorized a second booster dose of the Pfizer-BioNTech and Moderna coronavirus vaccines for people 50 and older and those 12 and older who are immunocompromised.

People in these groups are more likely to suffer severe outcomes if infected with covid, and officials say a second booster shot can help shore up their defenses and help keep them out of the hospital.

In most cases, the second booster will be a fourth dose of one of the mRNA vaccines. It may be a third shot for people who initially received a Johnson & Johnson vaccine, or a fifth shot for some immunocompromised people who needed three shots to complete their initial vaccination series.

The Centers for Disease Control and Prevention also updated its booster guidance Tuesday, paving the way for second boosters being available as early as Wednesday. The authorization does not extend to people under 50, who generally develop longer-lasting immunity from vaccines. The Food and Drug Administration plans to convene external advisers next week to debate a long-term booster strategy for the general population.

Here’s what you need to know about a fourth dose.